In many technical fields it is necessary to measure out precise amounts of one or more liquids and then supply them for a particular application. In the fields of chemistry and biotechnology, in particular, it frequently happens that one of several steps of a process in a reaction comprises measuring out finely metered amounts of a liquid and supplying them to the reaction. The term liquid here basically means any chemical substance which is present in liquid form.
The measuring out and supplying of liquids may be done manually using pipettes or with other intermediate storage elements. However, such manual proceedings require an operator and are also usually very time-consuming. For this reason the manual measuring out and supplying of liquids is usually only used at the experimental stage or for very low repeat rates. In applications where the repeat rate is very high or where very uniform measurement and supplying of one or more liquids is required, possibly at identical times, attempts are usually made to automate the process. Thus, for example, the “Biorobot 9600” system produced by the present applicant has been on the market for some years for carrying out molecular-biological processes such as the washing and extraction of nucleic acids or the isolation of RNA and/or DNA.
Thus, in order to produce highly purified DNA plasmids, a number of steps are carried out one after another, the individual steps being carried out at different, precisely fixed intervals of time relative to one another. First of all, cell cultures are placed in containers such as individual or multiple test tubes using an individual pipetting device. The cell cultures are put back into suspension and lysed. Then the cell cultures in solution are transferred into other containers using the pipetting apparatus. This is usually followed by filtration to purify the lysates. Filtering is carried out using special containers which have suitable filter elements set into their bases. A vacuum can be applied to the containers through an opening in the underside of the containers, through which the solution is sucked through the filters and thus filtered. Alternatively, the samples may also be centrifuged to separate them in a conventional but time-consuming manner. After the filtering, the DNA is adsorbed by means of a suitable membrane in another step. The DNA-free solution remaining can be removed by a rinsing process. The desired DNA is then recovered by a subsequent elution step.
The dispensers known from the prior art are generally in the form of individual dispensers, so that the measuring out and supplying of a liquid to a plurality of containers can only be carried out sequentially, i.e. one after another. The measuring device itself usually consists of a flexible tube in which a liquid pressure is built up using a pump. Just in front of the outlet from the flexible tube there is generally a valve which is briefly opened as required. The quantity of liquid flowing through the valve is accordingly directly dependent on the preliminary pressure prevailing in the flexible tube. Particularly if the valve is opened frequently at different time intervals, depending on the pump power between the individual valve opening processes, the pressure is not built up completely to the nominal pressure. Accordingly, the preliminary pressure prevailing in the line fluctuates substantially in some cases, with the result that uneven amounts of liquid are dispensed.